KR0133027B1 - Large sized guartz glass tube, large scale quartz glass preporm, process for manufacturing same and guartz glass optical fiber - Google Patents

Abstract

The present invention provides a quartz glass tube having an outer diameter of 50 to 300 mmφ, an outer diameter / inner diameter ratio of 1. 1 to 7, a thickness of 100 mm or more, and a thickness error of 2%, obtained by mechanically processing a natural or synthetic quartz glass base material; The large quartz glass preform obtained by integrating the large quartz glass tube by the rod-in-tube method on the core glass rod for the optical fiber and the mechanical processing are carried out with high precision as a large machine, and if necessary, heat treatment and heat stretching by a non-contact type heat processing method. Another aspect of the present invention provides a method for manufacturing a quartz glass tube for controlling a diameter by heating and stretching, and a large quartz glass preform integrating a core glass rod for an optical fiber by a rod-in tube method.

Description

Large quartz glass tube, large quartz glass preform and its manufacturing method used in quartz glass preform for optical fiber manufacturing and quartz glass optical fiber

1 is a cross-sectional view of a large quartz glass tube of the present invention,

2 is a cross-sectional view of a large size quartz glass preform for single mode of the present invention manufactured using a large size quartz glass tube,

3 is a schematic cross-sectional view of an optical fiber manufactured from the preform for single mode optical fiber of FIG.

4 is a conceptual diagram of refractive index distribution and light intensity distribution of a single mode optical fiber,

5 is a partial longitudinal cross-sectional view showing a method for manufacturing a large quartz glass tube according to the first embodiment of the present invention, wherein the large quartz glass tube is manufactured by a core drill perforator;

6 is a schematic view showing a method for producing a large quartz glass tube by a hot carbon drill press-fit method, which is a method for manufacturing a large quartz glass tube of the present invention;

7 is a schematic diagram showing a method of manufacturing a large quartz glass heat treatment tube by heat treatment of a large quartz glass element tube, which is a method of manufacturing the large quartz glass tube of the present invention, as a contactless heating method.

* Explanation of symbols for main parts of the drawings

1: core glass rod 2: a cladding layer

3: quartz glass tube 4: core

5: an optical cladding layer

7: quartz glass mother material

8: core drill 9: a grinding stone

11: carbon drill 13: heating heater

15: a heating source 16: a drawing roll

17: a dummy tube 19: sensor

The present invention is a large diameter, thick, thick quartz glass tube, small eccentricity, excellent transmission characteristics, and also can be mass-produced, inexpensive glass preform for optical fibers, in particular for quartz glass tube and single mode Large quartz glass tubes used in quartz glass preforms for the manufacture of optical fibers incorporating an optical fiber core glass rod by a rod-in-tube method, and methods for manufacturing the same, and also obtainable from the preforms. It relates to an optical fiber.

Recently, a large amount of optical fibers have been used in accordance with the practical use of quartz glass optical fibers, especially single mode optical islands.

The main manufacturing method is J.PA. No. Vad bum (weather failure method) described in 50-101416 etc., U.S.P. NO. OVD method (external method) described in 3932162 et al., U.S.P.No. There is an MCVD method (internal method) described in 4217027, etc., and almost all of the world market is occupied by products made by these three types of manufacturing methods.

However, it can be predicted that a large amount of optical fiber is required in the stage where the optical fiber is used for general subscribers in long distance trunks, but the above-mentioned three methods known in the art are limited even in terms of productivity and unit cost. You can think of it as reaching.

Since the research on the quartz glass fiber has been over 20 years, the transmission characteristics and the practical reliability have already been reviewed. Therefore, the development of a new manufacturing method that can maintain this characteristic and can be mass-produced and inexpensive is not possible. It is difficult.

In order to achieve mass production and cost reduction, it is considered that if the preform is enlarged and the productivity of the device is increased, mass production and cost reduction can be achieved, and at the same time, the cost can be expected to be lowered in evaluation cost and defects.

However, the above three methods have been examined with a focus on characteristics, starting from a small laboratory scale, and thus excellent in optical fiber characteristics, but have problems in mass production and inexpensiveness, and the fiber length that can be produced in one preform is In the MCVD method, 15 km to 30 km, the VAD method and the OVD method were limited to 100 km to 200 km.

Certainly, the above three manufacturing methods are suitable for manufacturing the transmission part of the optical fiber, but simultaneously manufacturing the clad part CLAD is not a proper method in terms of mass productivity and cost reduction.

For example, in graded index fiber or single-mode fiber, a cladding portion, which occupies 80% or more of the optical fiber cross-sectional area, is manufactured by using another method that is highly efficient and inexpensive. In combination with the three manufacturing methods, it is believed that an excellent manufacturing method is achieved.

For example, it is already performed to synthesize | attach a clad part by OVD method on the core glass rod made of VAD method, and to use it as a core glass rod for optical fibers.

However, in this conventional method, since a thin and short core glass rod is used, the cladding composition rate of the clad is low, and since it is synthesized for each core glass rod, there is a limit in mass productivity and cost reduction. The inventors of the present invention have newly examined the conventional method, and as a result, the core glass rod and the cladding part are separated, and the core glass part is made of the above-mentioned high performance core glass manufacturing method known in the prior art, and the cladding part is made by a separate method having high efficiency separately. By combining them, the above problems can be solved and the rod in tube method is optimal.

However, there is a problem with the conventional tube method which is a rod. First, there was a problem with the dimensions of the quartz glass tube. Conventionally, the size of the quartz glass tube used was small diameter (outer diameter 15-30 mm, thickness 1-6 mm), and the dimensional accuracy was about 10% in outer diameter, and 20 to 30% in thickness. When the core glass rod was inserted into the tube by the rod in tube method, a clearance of several millimeters was required for the purpose of preventing contact with the inner wall of the glass tube depending on the length, size, and skill.

For this reason, the diameter becomes thinner, the dimensional error of the tube increases, and the need for a wider gap overlaps, resulting in an eccentricity in the preform integrated by the rod-in tube method, which results in a large eccentricity of the optical fiber, In particular, in the case of assuming a coupling loss in a batch multicore connection construction of single mode fibers, the rod-in tube method was a manufacturing method without merits.

On the other hand, even if the core glass rod loaded into the stone glass tube is made under the same conditions, the characteristic varies depending on the variation, the fiber specification, the user's characteristics, and the manufacturing method. In response to these conditions, high-precision quartz glass tubes of various dimensions are required. It is excellent in terms of dimensional accuracy to make each of these high-precision quartz glass tubes by mechanical grinding, etc., but it requires a lot of working time, making it difficult to mass-produce and reduce the cost. However, it was difficult to manufacture a quartz glass tube with a target dimension that was poor in dimensional accuracy and greatly amplified at the time of heating and stretching.

In addition to the above problems, the rod in tube method has drawbacks such as mixing of foreign matter and generation of bubbles on the fusion surface between the inner surface of the quartz glass tube and the outer surface of the core glass rod. This depends on the atmosphere and the cleaning method at the time of the rod in tube method, but there is also a problem in the internal finish of the quartz glass tube.

The present inventors have diligently studied the problems of these phenomena, and as a result have improved and enlarged the above three methods which are currently performing well, a large diameter, thick high precision quartz glass tube and a large optical fiber core glass rod are used as a rod in tube method. When the large-scale preform integrated with the device is found, the quality of the eccentricity and the like in the single mode optical fiber is improved, and the mass production and the cost reduction are satisfied at the same time. In addition, the general problems related to the rod-in tube method, if a large quartz glass ingot or tubular body is used, a fixed large industrial machine can be used, for example, a drilling machine (trade name, ueda Technical institute) Internal and external surfaces are mechanically ground and drilled into the precision honing device described in Core Drill Drilling Machines, Outer Grinding Machines, and Ultra-Precision Machining Techniques (Ultra-Precision Machining Research, Industrial Society, page 421, 1984). It is possible to obtain a substantially high-precision large quartz glass tube by grinding, polishing, finishing to an exact dimension, and etching an annealing to remove surface contamination, and to reduce roughness and processing distortion of the cutting surface. Also, quartz glass pipes opened in the processing industry (hereinafter referred to as "carbon drill press method") that press and heat the high-precision machining in combination are heated, and the application technique of high purity silica is described on page 106. The quartz glass heat-treated tube heat-treated by the contactless heat treatment described above also has good dimensional accuracy. By combining the large quartz glass tube made of the above manufacturing machine and the core glass rod for the optical fiber, it is possible to integrate the rod in tube method so that many problems can be solved and it is possible to make a large preform, and 3000km as one preform. It has been found that the above-described high quality optical fiber can be easily manufactured continuously. In particular, the best characteristics can be obtained when the raw material is a synthetic quartz glass whose foreign material and impurities in the quartz preform are removed, dehydrated, and whose refractive index is adjustable. Based on this finding, the present invention has been completed.

An object of this invention is to provide the high precision large diameter and thick quartz glass.

It is an object of the present invention to provide a large-size quartz glass preform in which mass production is good and in which an inexpensive optical fiber can be manufactured.

It is an object of the present invention to provide a fixed large-size quartz glass preform that enables production of high quality optical fibers.

An object of the present invention is to provide a high quality optical fiber obtained from a large quartz glass preform.

An object of this invention is to provide the high precision large diameter and thick quartz glass tube used for the quartz glass preform for optical fiber manufacture.

An object of the present invention is to provide a method for producing a large quartz glass preform using the high precision large quartz glass tube.

The large-scale preform of the present invention, which achieves the above object, has a small eccentricity, generates little bubbles at the rod, tube, and interface, and further satisfies mass production and reduction in cost, thereby making it possible to manufacture high-quality optical fibers. It is to be done.

The present invention for achieving the above object is a rod-in a large Seoyoung glass tube having an outer diameter of 50 to 30 mm, a thickness of 10 mm or more, a ratio of the outer diameter to the inner diameter of 1.1 to 7, and a thickness error of 2% or less, and a core glass rod for an optical fiber. The large-size quartz glass preform is a high-precision grinding process of the outer surface or the inner surface of the quartz glass base material, and then the inner surface of the large glass preform integrated with the tube method and the optical fiber obtained by preselecting it. It is manufactured by integrating a large quartz glass tube and a core glass rod for optical fibers by a rod in tube method through a manufacturing process of finishing roughness to 20 μm or less.

Here, the terms used in the present invention are defined.

1) "Large quartz glass tube" is a generic term for tubular quartz glass, and the present invention also includes natural quartz glass tubes or synthetic quartz glass tubes made for rod-in tubes.

2) `` Quartz glass base material '' is a long columnar ingot or columnar large quartz glass made of high-purity natural quartz glass or synthetic quartz glass, and roughly ground as necessary, but processed to a target dimension. It means quartz glass before becoming.

In particular, synthetic quartz glass includes OH group control and refractive index (n) control (refractive index difference Δn within 0.02%) to meet the quality design of the optical fiber.

3) `` Quartz glass tube '' means a cylindrical quartz glass base material mechanically ground and drilled by a coder drill perforator, or a tube or tubular large quartz glass base material made by a carbon drill indentation method, It refers to a large quartz glass tube whose surface or inner surface is mechanically ground and ground to roughly the target value.

4) `` Quartz glass tube '' means the inner and outer diameter of quartz glass tube accurately, thickness error is 2% or less, internal and external surfaces are polished and polished, and the surface roughness after HF-etching treatment. Refers to a quartz glass tube having a thickness of 20 μm or less.

5) `` Quartz glass heat-treated tube '' is a tube which is subjected to heat treatment, heat-stretching, or heating and pressure-computing processing in a non-contact type heat processing method after continuous quartz glass element pipe, and a large quartz glass tube in which the inner and outer surfaces of the tube are heat treated. Or it refers to the large-size quartz glass tube different from a quartz glass element pipe by extending | stretching process.

6) "Thickness error" means measuring the thickness of a large-size quartz glass tube of arbitrary length along its length direction (for example, by rotating it at least 5 points or at intervals of 50 to 100 mm) and measuring the maximum thickness (t) of the tube at that position ( tmax), the value at the minimum tmin, i.e., [(tamx-tmin) / (tamx + tmin) / 2}] x100 (%) Say

7) "Non-contact heating processing method" means that a dummy tube is fused to a quartz glass tube, and the dummy tube is held in a processor and passed through without being in contact with a heating region, thereby heating the quartz glass tube. Refers to treatment, heat stretching treatment or heat pressure stretching treatment.

8) The "optical fiber core glass rod" is an optical transmission part, which is composed of a core part and an optical clad part, and the clad part synthesized with the core part is sufficiently added for public communication such as single mode and multi mode for high quality purposes. It refers to a glass rod that does not become a fiber conforming to the standard, including only that coated with synthetic cladding and / or quartz glass tube by OVD method.

The large quartz glass tube is a large tube made of quartz glass that satisfies the quality characteristics required for the clad tube for general optical fibers and has an outer diameter of about 50 to 300 mm. The optical fiber obtained by reducing the dimensional error of the large diameter and thickened quartz glass tube, and using the pre-made large preform made by the rod-in tube method, can reduce the eccentricity, which is effective for mass production and cost reduction. Because the outer diameter is large and the outer diameter / inner diameter is too thick, the absolute value is also large, and the processing accuracy is large, so that the error becomes large even when the outer diameter and the outer diameter / small diameter are small, and the reaction tube for MCVD and the multi-coating are close to the core. High accuracy is required for caliber and thin pipes.

The cross sectional view of the large quartz glass tube of this invention is shown in FIG. 1, and the cross sectional view of the large quartz glass preform of this invention is shown in FIG.

In FIG. 1, Do is an outer diameter, Di is an inner diameter, and in FIG. 2, 1 is a core glass rod, 2 is a cladding layer, and 3 is a coated large quartz glass tube.

FIG. 3 shows a cross-sectional schematic diagram of an optical fiber, such as a single mode fiber, obtained by prescribing the above-mentioned large-size quartz glass preform. In FIG. 3, 4 is the core, 5 is the optical clad, 6 is the over clad, a is the core diameter (d core), b is the optical clad diameter (d cladi), c is the outer diameter of the optical fiber ( d clado) 125 μm.

4 shows a schematic of the refractive index distribution and Power distribution of a single mode fiber.

In FIG. 4, the optical cladding portion is a portion in which the optical power distribution outside the d core is formed wide. Therefore, the optical cladding (d cladi) is composed of the cladding at the same time as the synthesis of the core, the thickness of the core varies depending on the conditions such as the shape of the distribution, refractive index difference (△ n), fiber usage, etc. In practice, the value multiplied by the safety factor is adopted. In the present invention, the quartz glass core rod for an optical fiber refers to a quartz glass rod including at least an optical clad portion of FIG. 4.

In the present invention described above, the optical fiber is formed by selecting a large preform, so that the ratio d clado / d cladi between the outer diameter (d clado) of the optical fiber of FIG. 3 and the optical clad diameter (d cladi) is the large quartz glass of FIG. It is generally proportional to the ratio Do / Di of the outer diameter Do and the inner diameter Di of the large quartz glass tube of FIG.

Therefore, in designing an optical fiber, it is necessary to design Do / Di mentioned above as an index. For example, when the power diameter of a single mode fiber (for 1.3 μm wavelength) is 9 μm, the power diameter of a GI multimode fiber is 50 μm, and the outer diameter of the optical fiber is 125 μm, Do / Di has the values shown in Table 1 below. .

According to Table 1, for example, in the case of the multi-mode fibers shown in parentheses, Do / Di is 2.5 or less, and usually 5 to 30% of the synthetic cladding layer, for example, 20% of the cladding layer by co-synthesis. 60 µm and Do / Di = 2.08.

In the case of single-mode fiber, a practical optical fiber is obtained when Do / Di is about 7 or less. That is, the main power distribution, such as 1.55 μm substitute (dispersion type) and 1.3 potential substitute (combined cladded type) (matched cladded type) (deplest type), is estimated to be about 20 μm or less. Even if a safety factor is adopted, the practical range is d cladi / d core # 3 or more, that is, Do / Di # 4.63 or less. In the case of double or triple jacketing, Do / Di is also less. However, selecting Do / Di in the range of 1.1 to 7 is a condition for producing a practical optical fiber. However, since Do / Di is a ratio of the preform diameter, it is needless to say that in the case of the quartz glass tube for rod-in tube, it is necessary to make a slight gap between the quartz glass tube and the core glass rod.

In order to make a large quartz glass tube, a kind of method known to the case of natural quartz is used. Pot melt drawing method and mold molding method are also available, but large diameter hardening is difficult in the pot melt drawing method, and in the mold molding method, the heat-resistant material used for the container is directly contacted and melted with quartz glass for a long time to remove impurities in the heat-resistant material. Transfer and spread to the inner and outer surfaces of the quartz glass base material.

Therefore, since the transmission loss of the optical fiber is increased, it is necessary to greatly remove the contaminated portion when the core portion is approached and coated.

In the method for producing a large quartz glass tube according to the present invention, a columnar quartz glass base material is made, and the center thereof is opened by mechanical grinding using a core drill perforator shown in FIG. 5 or a columnar quartz glass base material. Is a two-stage process, such as opening through short-term contact melting by hot carbon drill indentation method, or OVD method (USP No. No. 2) in which a porous silica soot material is deposited on a heat-resistant core material and dehydrated and melted. 2, 272, 342, or the one-step method of making a soot by direct VAD method, dewatering and fusion glass, etc. are available. In FIG. 5, 7 represents a columnar quartz glass base material, 8 represents a core drill, and 9 represents a grindstone. FIG. 6 shows a schematic diagram of the hot carbon drill press-fit method. In FIG. 5, 10 is a columnar quartz glass base material, 11 is a carbon drill, 12 is a quartz glass source, and 13 is a heater.

If the size of the quartz glass tube for rod in tube is poor, the error is further amplified during the heat drawing process, and the error becomes relatively large.

In addition, since the error becomes larger due to multiple coatings, the dimensional accuracy needs to be accurate. Mechanical grinding is suitable for processing quartz glass base materials and obtaining high precision quartz glass tubes. With the increase in size of quartz glass, mechanical softening, in particular, precision grinding by industrial large-scale machines known up to now becomes possible.

However, while a high degree is obtained, processing grooves, fine cracks, grizzles, processing distortions, etc. at the time of grinding are generated on the processing surface, and when they are integrated by the rod-in-tube method, bubbles are generated at the inner boundary surface. In order to solve such problems in the related art, internal roughness may be formed by time-consuming high-precision mechanical grinding, internal surface polishing or fire polishing, or by forming a special glass layer on the inner surface to form the inner surface. Although it is about micrometer (refer to JAP 52-92530), this process was cumbersome and it was hardly implement | achieved when mass-producing large size (large diameter, thick thickness, long length) quartz glass tube. However, it has been found that the internal finish of high purity quartz glass tubes can be solved by using a precision honing device.

In this processing method, if the quartz glass tube is 50 mm φ or more in outer diameter, the full length of the round tube of about 3000 mm is straight, so that the round tube can be processed at the entire position.

Grind and grind by changing the grade of grindstone or grindstone, remove cracks, grizzles, torsion, etc., and treat it with a single hydrofluoric acid solution to relieve stress concentration and ultrasonic cleaning If removed, the inner roughness is 20 µm or less, and if necessary, the material is heat-processed to obtain sharp edges of the mechanical grinding part and a smooth surface of the cracked part, and at the same time, to solve the processing distortion, It is possible to suppress the occurrence.

According to the experiments of the present inventors, when the inner surface roughness exceeds 20 µm by grinding, even when heated and stretched, the processing defects are not alleviated or released, and bubbles are generated at the inner boundary surface when being integrated by the rod in tube method. It became known.

In the case of a quartz glass tube in which a cylindrical quartz glass base material is mechanically ground by a core drill perforator, or mechanically precisely ground the inner surface of a tubular large quartz glass base material made by OVD, etc. Honing is good. As a result, it is possible to narrow the gap with the core glass rod. This ultra-precision honing and outer grinding are combined to make the thickness error of the grinding tube less than or equal to 2%. In the error within this range, the amplification of the error at the time of hot press stretching hardly occurs, and the eccentricity of the fiber is not adversely affected.

The hot carbon drill indentation method heats a columnar quartz glass base material and indents a carbon drill in the center. However, when the thermal opening method of this method is adopted, the inner roughness of the quartz glass tube is 20 µm or less without grinding or polishing. In fact, there is an advantage that can easily form a large quartz glass tube of several micrometers or less. Moreover, when the outer diameter of the target quartz glass base material is 50 mmφ or more, the degree of roundness, straightness, etc. of an opening part can be improved remarkably. Therefore, in the columnar quartz glass base material with an outer diameter of 50 mmφ or more, the whole diameter is aligned in a straight line in a large diameter tube having an outer diameter of 300 mmφ or more and a length of about 3000 mm by opening by the hot carbon drill press-fitting method. It is possible to produce a round tube from.

The grinding of the outer circumferential surface does not have to be more severe than the grinding of the inner circumferential surface because the grinding surface is directly heated to the high temperature part, but since it is an optical fiber, the breaking strength is affected. The surface roughness must be at least 200 µm or less, preferably 100 µm or less. For this reason, for example, a standard outer circumferential grinding machine or cylindrical grinding machine, which has a track record of semiconductor ingots and various ceramic grinding processes, is used for outer circumferential grinding.

After finishing the above-mentioned life-saving processing, it is confirmed that the thickness error is less than 2% by finishing polishing of the machined surface. The hydrofluoric acid etching treatment is performed to obtain a quartz glass tube having a surface roughness of 20 µm or less. The quartz glass tube is integrated with the core glass rod for optical fiber and the tube-in-rod method. However, even if the core glass rod is made under the same conditions, the characteristic varies depending on variations, fiber specifications, consumer characteristics, and manufacturing methods. Therefore, in order for the quartz glass element to be combined with the core glass rod, it is preferable to heat-treat the quartz glass tube of various dimensions. For this heat drawing treatment, a contactless heating method in which impurities are not adhered to the quartz glass tube can be used.

In Fig. 7, 14 denotes a quartz glass tube, 15 a heating source, 16 a draw roll, 17 a dummy tube, 18 a quartz glass heat treatment tube, and 19 a sensor. In the non-contact heating method, it is necessary to pressurize the tube at the same time as to stretch the large-size quartz glass tube to the exact target dimension. The pressure should be changed according to the size, thickness of the quartz glass tube, glass viscosity at heating, elongation ratio, etc., but in order to obtain a more accurate dimension, the ratio of the outer diameter (Do) and the inner diameter (Di) of the quartz glass tube is (Do / Di). And the ratio (do / di) of the outer diameter (do) and the inner diameter (di) of the quartz glass heat treatment tube after the heat-stretching treatment is processed so as to be in the range of (do / di) / (do / di) = 1.0 to 1.5. Good to do.

If the electrical ratio is 1.0 or less, the shape of the tube is accompanied by deformation, and if it exceeds 1.5, the thickness error of the tube increases, and the tube ruptures according to the temperature conditions. Therefore, it is impossible to make a quartz glass tube with an accurate dimension outside the treatment range.

In particular, it is absolutely necessary that the thickness error be less than or equal to 2% when the ratio is close to 1.5. Further, the temperature of the heat treatment treatment is 1600 to 3000 ° C, preferably 2000 to 2800 ° C for economic reasons, depending on the outer diameter of 50-300 mm.

Below the above temperature range, it is difficult to heat-soften the quartz glass tube, or above the electric temperature range, the quartz glass tube becomes deformed and flexible with deterioration, and it is difficult to accurately maintain the dimensional accuracy.

Do / Di or do / di denotes an over cladding portion of a single-mode optical fiber, and in the case of one jacket, the ratio is 2 to 7, and when the coating is performed two or more times, for example, those of about 1.1 to 3 are combined. .

Since the above-mentioned heat-treated quartz glass heat-treated tube is heat-treated at a high temperature of 1600 to 3000 ° C., various processing defects such as roughness of the grinding surface and processing torsion based on mechanical grinding are alleviated or released. In particular, as the degree of thermal stretching is large, the surface flaws, cracks, pits, etc. are greatly deformed and enlarged, so that holes are shallow, sharp corners are eliminated, and high precision mechanical polishing required for quartz glass tubes for tubes that are conventional rods is performed. It is possible to omit a process treatment that is not suitable for mass production, such as treatment, hot polishing of the inner surface, or treatment of forming a special glass layer on the inner surface. Therefore, it is advantageous to make a large quartz glass tube with high accuracy and to obtain a desired large quartz glass tube using heat deformation.

In the method of manufacturing natural quartz glass according to the present invention, the high-quality part is selected from natural quartz glass, the outer part of each quartz glass is removed, the center part is taken out, and it is crushed to cut the particle diameter and remove foreign substances. Chemical treatment removes impurities. The raw material is manufactured by a method known from the past, such as a pot melt drawing method and a mold forming method. However, the method of producing a large columnar quartz glass base material by the Verneuil method by Oxyhydrogen is the least impurity and is recommended as a manufacturing method of the quartz glass material for optical fibers.

In the method for producing a synthetic quartz glass ingot or tubular body used in the present invention, various production methods described in the above-mentioned "Application Techniques for High Purity Silica" Nos. 100 to 104, which have been known so far, can be considered. It is a method to obtain glass ingot directly by gaseous silicon compound such as SiCl and oxyhydrogen frame, and contains 800 ppm or more of OH groups in synthetic quartz glass (for low OH). It is inappropriate for the following, and is used only for photomask substrates for semiconductors and optical members of exposure apparatus.

In addition, the plasma method improved from this method is used only for the manufacture of special products such as high-purity core glass for optical fibers, because the OH group is low and the unit price is increased due to the high power demand.

On the other hand, the direct glassing method also lowers the flame temperature, attaches the raw material gas to the rotating substrate (target) by blowing it, and forms a porous soot material, followed by dehydration treatment. It is suitable in the manufacturing method of the base material of this invention since there is no.

The VAD method mainly produces a solid columnar quartz glass base material, and the OVD method produces a tubular quartz glass base material directly.

In the synthetic quartz glass tube adopting the manufacturing method according to the soot method, it is possible to be combined with the cladding portion of the core glass rod to be used to accurately match the refractive index of the OH group.

In the large quartz glass preform of the present invention, the large-diameter preform of 75 mmψ or less may be formed using a quartz glass tube of about 75mmψ to make a preform, to re-extend the large preform, or to a rod-in-tube process. It is possible to obtain the preform of the target outer diameter directly by simultaneously merging and stretching the core glass tube in the same process.

Selection of characteristics such as mode field diameter, cutoff wavelength, and dispersion is important for the core glass rod for single mode. In recent years, even when the core glass rods are used as they are, the characteristics are often scattered slightly.

Therefore, after adjusting the cladding thickness of the core glass rod once in the quartz glass tube, the characteristic check is carried out, and the large-size quartz glass tube is jacketed a second time, and the outer diameter is controlled by combining etching. do. Large quartz glass preforms are characterized in that the adjustment range is extended to obtain a high degree again.

Example 1

Using the axial method (VAD method), SiCl was vaporized, hydrolyzed in oxyhydrogen salt, and sprayed on a rotating quartz glass rod to form a large quartz porous glass material. The glass material is placed in an electric furnace, and heated and dehydrated by a mixture of He and Cl in consideration of the conditions of the core glass rod, and transparently formed at 1550 ° C. according to a zone melt method. It is made of base material. The quartz glass base material is first cut at both ends, and then alternately opens the center from both ends in a core drill drill of # 80 grindstone, and then roughly ground at the outer peripheral grinder of # 80 grindstone to adjust dimensions. A synthetic quartz glass tube having a diameter of 94 mm, an inner diameter of 30 mm, an outer diameter / inner diameter = 3.13, a thickness of about 32 mm, a length of 730 mm, and a weight of about 10 kg was obtained.

The inner surface of the synthetic quartz glass tube is processed in a long automatic honing machine for ultra-precision finishing, to obtain a synthetic quartz glass tube having a round hole through the entire length, and then the inner diameter center and outer diameter center in the NC outer grinding mill. The outer circumferential surface was ground so as to coincide with this, the inner and outer grinding and polishing were repeated until the thickness error was 2% or less, the inner end was finally finished with # 800, and the outer circumference was trimmed with # 140. To remove the surface contamination and to reduce surface distortion, the surface of the quartz glass tube is etched and polished with hydrofluoric acid with a concentration of 30% to 50%, and ultrasonically cleaned in pure water. A glass tube was also obtained.

This synthetic quartz glass tube has an outer diameter (Do) of 91.5 mm, an inner diameter (Di) of 32.4 mm, an outer diameter (Do) / inner diameter (Di) ratio of 2.82, a thickness of 29.55 mm, a thickness error (tmax-tmin) of 0.48 mm ( 1.62%), length 730 mm, and weight 9.2 kg.

Furthermore, the surface was moved 8 mm in the longitudinal direction with a tacky simple illuminometer to obtain an inner roughness (Rmax) of 4.8 µm and an outer roughness (Rmax) 53.

On the other hand, a 1.3 mu m single-mode glass rod having an outer diameter of 54.5 mm ψ and a length of 455 mm was prepared from the core, the clad refractive index difference (Δn) = 0.343%, and the rod of the clad portion in accordance with the VAD method. An external fisherman precision automatic stretching machine was heated and stretched to an outer diameter of 30.1 mm, designed to have a cutoff wavelength lambda c of 1.25, slightly etched the outer surface of the roller, and blow cut to a length of 730 mm. After carefully inserting the core glass rod into the synthetic quartz glass tube carefully, the centers of the core glass rod and the synthetic quartz glass tube are matched to each other and fixed, and both ends thereof are connected to a dummy quartz material. By rotating, the bending and torsion of the splicing process were corrected.

This was inserted into the vertical electric furnace from the top, and the tip was welded at 2180 ° C., and the pressure was reduced with a vacuum pump.

The moving speed was changed while adjusting the temperature (2000-2800 ° C.) and the vacuum degree (200-1000 mm water column Aq), and the bubble conditions at the interface were adjusted. In the absence of foaming, the full length was gradually moved to 2 mm / min. To make a preform.

The preform part obtained under stable conditions was 90.2 mm in diameter, 595 mm in length, and 8.3 kg in weight, and was about 300 km in fiber length. A portion of the preform was stretched to an outer diameter of about 50 mm φ and irradiated with a preform analyzer. As a result, at the boundary between the rod and the clad layer, the step difference in refractive index was almost 0.01% or less, and the eccentricity was 0.153 mm (0.43%).

In addition, when a fiber having an outer diameter of 125 µm is made about 5 km by fiber picker and the fiber characteristics are examined every 1 km, the transmission loss at the eccentricity is 0.22 µm, the cut-off wavelength (λc) 1.285 µm, and 1.3 µm. The OH group loss at 0.355db / km and 1.38㎛ was 0.86db / km, and it can be seen that it has excellent characteristics with respect to the single mode optical fiber.

Example 2

As in Example 1, the outer diameter (Do) 93.5 mm ψ, inner diameter (Di) 31.6 mm ψ, Do / Di = 2.96, thickness 30.95 mm, thickness error (tmax-tmin) 0.42 mm (1.36%), length 700 mm, A synthetic quartz glass tube with a weight of 9.3 kg was made. The surface of this synthetic quartz glass tube was moved 8 mm in the longitudinal direction with a melt immersion roughness meter, and as a result, it was 8.5 micrometers of inner surface roughness (Rmax), and 68 micrometers of outer surface roughness (Rmax).

The synthetic quartz glass tube is heated in a vertical electric furnace to heat 2200 ° C., inert gas is introduced into the inside and outside of the tube, and the bottom part is welded and press-drawn by the non-fusion heating method shown in FIG. Made of synthetic quartz glass heat-treated tube.

On the other hand, the core glass rod for single mode of refractive index difference ((DELTA) n) = 0.335% was prepared by the VAD method. After hot stretching, the synthetic quartz glass heat-treated tubes shown in Table 2 were respectively calculated as clad layers, and the outer circumference of the core glass rod was etched to obtain the core glass rods shown in Table 2.

When the respective core glass rods were inserted into the respective synthetic quartz glass heat treatment tubes, and the heating was integrated in an electric furnace and measured with a preform analyzer, the step of refractive index between the clad layers could not be recognized.

No. of Table 2 When a 125 µm optical fiber element wire was prepared using 3 (62 mm) preform and the fiber characteristics of the element wire were examined, the cut-off wavelength (λc) was 1.245 µm, 1.3 µm transmission loss 0.334 dB / km, and eccentricity 0.32 µm. It was a high quality fiber optic.

Example 3

A large porous soot base material is made by the axial method (VAD method), and according to Example 1, it is heated and dehydrated and made into transparent glass, rough grinding, outer diameter 96 mm ψ, circumferential quartz glass of about 820 mm length A base material was obtained.

The quartz glass base material was punched in the center by using a hot carbon drill indentation method, and the outer periphery was ground and hydrofluoric-treated to increase the dimensional accuracy. The synthetic quartz glass tube at this point had an outer diameter of 101 mm, an inner diameter of 40 mm, and an outer diameter / inner diameter ratio of 2.525. It was 775 mm in length and weighed about 11.5 kg. Since the inner surface of this tube formed a hole by heat melting, mechanical shock, cutting breakage, cracking, machining stress, and processing distortion were not recognized.

Then, for the purpose of investigating the inner surface roughness of the synthetic quartz glass tube, the polishing roughness of the honing machine was changed and polished every 150 mm in length, and the samples shown in Table 3 were obtained by etching. A core glass rod of about 38 mm φ was inserted into the synthetic quartz glass tube, and preformed in the same manner as in Example 1.

The interface state is shown in Table 3.

Example 4

By the external method (OVD method), a large porous soot base material was made, glass was formed by dehydration and refractive index adjustment treatment, and a synthetic quartz glass base material of a cylindrical shape was made. Both ends were cut in parallel and roughly circumferentially ground in an external grinding machine with a # 80 whetstone. After reaching the target outer diameter, it was installed in a honing machine and internally polished using a # 80 whetstone. Subsequently, the grinding wheel was changed to # 140, # 400, and # 800 for polishing. It was then rotated by an ultrasonic thickness gauge every 50 mm in length to measure the thickness of 8 points per revolution, and moved sequentially. The thickness variation of the electric field was investigated, and the thickness error was plotted by a computer. Based on this, the outer circumference was polished and corrected in an NC outer grinder, and the hydrofluoric acid etch was performed after confirming the thickness. This large synthetic quartz glass tube has an outer diameter of 164 mm, an inner diameter of 58.9 mm, an outer diameter / inner diameter ratio of 2.78, a thickness of 52.55 mm, a thickness error of 440 μm (0.84%), a length of 1870 mm, a weight of approximately 75 kg, and surface roughness ( Rmax.) 3.5 µm and an external surface roughness (Rmax.) 77 µm.

On the other hand, this synthetic quartz glass tube was assumed, and the large sized single-core quartz core glass rod was created by the VAD method, and three sets with substantially the same characteristics were set. The core diameter required for this synthetic quartz glass tube was calculated by calculation of the cut-off wavelength lambda c, and a part of the clad portion of the core glass rod was etched and adjusted. Then, this core glass rod 3 was welded, stretched to about the same outer diameter (55 mm), and after etching, the whole surface was hot-polished (fire-polish).

The core glass rod is placed in the large synthetic quartz glass tube to fix the lower end, and the core glass rod is placed in a vertical electric furnace, heated at a temperature of 2000 to 2800 ° C. to melt and soften from the lower end, and a temperature and vibration degree (200 to 1000 mm Aq). Moved while adjusting, and the rod-in tube. If the temperature is not appropriate and the speed is high, since the foam bubbles remain at the inner boundary surface, it is first drawn to the outer diameter of about 50 mm ψ and the boundary surface is sufficiently wetted and welded, and 75 mm ψ, 100 mm ψ, 125 mm ψ is confirmed. The preform was made into five kinds of sizes, and enlarged to 150 mmψ.

The obtained preform had an outer diameter of 152 mm, the total weight of the five preforms of about 71 kg, and was equivalent to 2600 km in terms of optical fiber strands.

In order to investigate the properties of the preform in detail, when a preform of 50 mm ψ is selected and the properties of the core are examined by the preform analyzer, a seam of about 0.008%, and a refractive index of the core clad interface can be seen and a refractive index ), And the center shift of the core and clad was 0.28%.

The 50 mm ψ preform was selected as an optical fiber cactus, and the outer diameter was 125 µm ± 0.5 µm, and the transmission characteristics of the element wire were obtained. As a result, the transmission at the pin core ratio of 0.11 µm, the cut-off wavelength (λc) of 1.270 µm, and 1.3 µm was obtained. Loss of OH group at 0.361 dB / km and 1.38 µm was 0.65 dB / km.

Example 5

In the same manner as in Example 4, an external method (OVD method) was used to make a large porous suit material, dehydrate and adjust the refractive index of the glass to make glass, and to form a synthetic quartz glass base material in a tubular shape. The surface was mechanically rough ground and four synthetic quartz glass tubes were made. After the inner diameter was finished in an ultra-precision honing machine, the outer circumferential surface was ground by artificially deviating from the centerline of the inner diameter and the outer diameter, and washed after hydrofluoric acid treatment. This synthetic quartz glass tube had an outer diameter of 100 mm, an inner diameter of 32 mm, and Do / Do = 3.125, and the measured errors were as described in Table 4.

The synthetic quartz glass tube was placed in an electric furnace, heated and stretched at a pressure of 2200 ° C. (pressurization: 0 mm to 100 mm), and the dimensions after processing were examined.

The results are shown in Table 5.

Condition A made the internal pressure and external pressure of an element pipe nearly the same pressure.

According to the said Table 4, the quartz glass tube with a large error will have a large error after stretching if the pressing ratio and calculation ratio become large.

In particular, the pressurization ratio directly changed the thickness error of the quartz glass tube significantly, and the elemental tubes of 3.9% were deformed to non-objects under unstable conditions at start, and then rapidly expanded and ruptured in the furnace.

Where α: do / di

β: (Do / Di) / (do / di)

In the synthetic quartz glass heat treatment tube, No. 13, the tube under the condition of B (that is, make the error of 1.8% of the elementary pipe, the tube after the heat-pressurized stretching is less than 2% error), insert the optical fiber core glass rod, preform by the rod in tube method Was written. When irradiated with a preform analyzer, the refractive index difference of the cladding part was 0.01% or less, the eccentricity after pretreatment was 0.45 µm, and there was no problem as a single mode fiber.

Example 6

The Bernoulli method by oxyhydrogen salts produced a large columnar natural quartz glass substrate. The quartz glass base material was subjected to a hot carbon drill press-fitting method according to Example 3, the outer periphery was trimmed by machining, washed with Foshan, and washed with water.

The quartz glass tube has an outer diameter of 170 mm, an outer diameter of 60 mm, an outer diameter / inner diameter ratio of 2.916, a length of 3 m, and a weight of 150 kg. When the thickness is irradiated at 50 mm intervals, the average thickness error is 0.3 mm. It confirmed that it was in a range. In addition, when the surface roughness at the quartz glass tube end was measured with a stylus simple roughness meter, the surface roughness (Rmax) was 0.8 µm and the surface roughness (Rmax) was 95 µm.

On the other hand, some clad-treated single mode optical fiber core rod made of VAD method was prepared, inserted into the quartz glass tube, and installed in a vertical electric furnace.

The temperature of the furnace was raised to 2250 ° C, the tip was melted, and then vacuumed to the upper portion. The conditions of the rod-in tube method were set by setting the vacuum degree 200 to 1000 mmAq and the start outer diameter to 50 mm ψ, changing the temperature, the moving speed, and the vacuum degree while viewing the interface fusion state between the core rod and the quartz glass tube. A preform having an outer diameter of 160 mm ψ was obtained.

The preform extracted with 50 mm ψ was measured with a preform analyzer. As a result, the eccentricity was 0.52%, and a slight step difference of -0.005% was visible in the cladding of the core glass rod and the quartz glass tube. Slightly lower.

The preform measured the optical fiber characteristics with a fiber of 125 μm in predecessor, the eccentricity was 0.41 μm, the transmission loss of 0.3 μm wavelength was 0.345 dB / km, and showed the characteristics that could be used as a single rod quartz glass fiber. .

Example 7

In the same manner as in Example 6, the center of the columnar quartz glass base material which can be made from high purity natural quartz glass was made by hot carbon drill indentation. Subsequently, the outer periphery was ground in accordance with the center of the inner diameter, and after confirming the dimensional accuracy, hydrofluoric acid etching, washed with water, and dried, the finished quartz glass tube was outer diameter 150 mm ψ, inner diameter 62 mm ψ, Outer diameter / inner diameter ratio = 2.42, length 2500mm, thickness super difference measured every 50mm in the longitudinal direction is 0.35mm (0.79%), inner surface roughness Rmax is 1 micrometer or less, outer surface roughness Rmax is 85 It was μm. In addition, the quartz glass was measured with an absorption spectrum of 2.7 占 퐉 as an infrared spectrophotometer and found to contain an average of 166 ppm of OH groups.

Then, the quartz glass tube was placed in a vertical electric furnace, and the temperature was raised to 2250 ° C to melt seal the lower end. Stretching was carried out by pressurizing with air from the upper end, and the outer diameter, the inner diameter and the thickness were examined to prepare a quartz glass heat treatment tube having an outer diameter of 50 mm, 75 mm, 100 mm, or 125 mm. The dimensions of each quartz glass heat treated tube are shown in Table 5.

From the center of the quartz glass heat treatment tube, a tube having an outer diameter of 100 mm φ was selected, a single mode optical fiber core rod was mounted by the VAD method, and integrated into the rod in tube method.

In the same manner as withdrawal conditions of the tube, three kinds of heat-treated tubes of 50 mm, gradually 75 mm, and 96 mm, were used for the initial outer diameter of the drawn out. When preforms of each dimension were cut and polished, and the fusion surface between the inside of the quartz glass tube and the outer surface of the core rod was observed and examined, almost no bubbles were found.

When the fiber properties were checked using a 50 mm ψ preform, the transmission eccentricity was 0.27 µm and the transmission loss of 1.3 µm was 0.347 dB / km.

Claims (23)

In the large quartz glass tube, (a) Outer diameter 50-300 mm: (b) the ratio between the outer diameter and the inner diameter which is generally proportional to the ratio of the outer diameter of the optical fiber to the optical cladding diameter is from 1.1 to 7: (c) a thickness of at least 10 mm; (d) thickness error 2% or less: and, (e) A large quartz glass tube used for a quartz glass preform for optical fiber manufacturing, characterized in that the inner surface roughness is 20 µm or less. 2. The large quartz glass tube according to claim 1, wherein the large quartz glass tube is made from high purity natural quartz glass or synthetic quartz glass. In the method of manufacturing a large quartz glass tube, (a) Perforate the quartz glass base material: (b) cutting, grinding and finishing the inner and outer peripheral surfaces of the opened base material; (c) hydrofluoricating the surface; And, (d) cleaning the base material subjected to the above process; A method of manufacturing a large quartz glass tube for use in a quartz glass preform for optical fiber manufacturing, comprising the steps, wherein the ratio of the outer diameter and the inner diameter is generally proportional to the ratio of the outer diameter and the optical cladding diameter of the optical fiber. The method of claim 3, wherein the large quartz glass tube (a) Outer diameter 50-300 mm: (b) the ratio between the outer diameter and the inner diameter is from 1.1 to 7: (c) thickness 10 mm or more; (d) thickness error 2% or less; And, (e) A method for producing a large quartz glass tube for use in a quartz glass preform for producing optical fibers, characterized in that the inner surface roughness is 20 µm or less. The method of claim 3, The quartz glass base material is a circumferential quartz glass base material or a cylindrical quartz glass base material, characterized in that the manufacturing method of a large quartz glass tube used in the quartz glass preform for optical fiber manufacturing. The method of claim 4, wherein (a) opening the quartz glass base material as a mechanical perforator; (b) cutting, grinding and finishing the inner and outer surfaces of the opened base material using an outer grinding machine and a precision honing machine; (c) hydrofluoricate the surface; And, (d) cleaning the base material having undergone the above process; A method for producing a large quartz glass tube used in a quartz glass preform for optical fiber manufacturing, comprising steps. The method of claim 4, wherein (a) opening the columnar quartz glass base material by annual carbon drill indentation; (b) hydrofluoricating the surface of the opened base material; And, (c) cleaning the base material subjected to the above process; A method for producing a large quartz glass tube used in a quartz glass preform for manufacturing optical fibers, characterized in that it comprises the steps. The method of claim 4, wherein The large-size quartz glass tube according to any one of claims 4 to 7 is again subjected to a ratio (Do / Di) of the outer diameter (Do) and the inner diameter (Di) of the quartz glass tube by using a non-contact heating process and heating. The internal pressure is controlled so that the ratio (do / di) of the outer diameter (do) and the inner diameter (di) of the quartz glass heat-treated tube after processing is set to (Do / Di) / (do / di) = 1.0 to 1.5. A method for producing a large quartz glass element used in a quartz glass preform for optical fiber manufacturing, comprising the steps of making a large quartz glass heat-treated tube by heat treatment, heat stretching or hot pressing stretching at 1600 to 3000 ° C. In the large quartz glass preform, (a) (1) outer diameter of 50 to 300 mm ψ; (2) ratio of outer diameter to inner diameter of 1.1 to 7: (3) thickness of 10 mm or more; (4) thickness error 2% or less; And (5) a large quartz glass tube having an inner surface roughness of 20 µm or less; and, (b) a core glass rod for an optical fiber integrally coupled to the large quartz glass tube; Large quartz glass preform, characterized in that it comprises a. 10. The large quartz glass preform of claim 9, wherein the large quartz glass tube is a high purity synthetic quartz glass tube having a refractive index within 0.02% of a design value. The method of claim 9, wherein the large Seoyoung glass tube; (a) opening a quartz glass base material; (b) cutting, grinding and finishing the inner and outer surfaces of the opened base material; (c) hydrofluoricating the surface; And, (d) cleaning the base material subjected to the above process; Large quartz glass preform, characterized in that it is manufactured according to the steps. 10. The method of claim 9, wherein the large quartz glass tube comprises: (a) mechanically opening a columnar quartz glass base material; (b) cutting, grinding and finishing the inner and outer surfaces of the opened base material with an outer grinding machine and a high precision honing machine; (c) hydrofluoricating the surface; And, (d) cleaning the base material through the above process; Large quartz glass preform, characterized in that the large quartz glass tube made according to the steps. 10. The method according to claim 9, wherein the large quartz flask is made of (a) a tubular quartz glass tube using the OVD method; (b) cutting, grinding and finishing the inner and outer surfaces of the tube, opened as an outer grinding machine and a mechanical drilling machine, and / or a precision honing machine; (c) hydrofluoricating the surface; And, (d) cleaning the base material through the above process; Large quartz glass preform, characterized by large quartz glass tubes made as steps. 10. The method of claim 9, wherein the large quartz glass tube comprises: (a) opening the columnar quartz glass base material by hot carbon drill indentation; (b) hydrofluoricating the surface of the opened base material; And, (c) the process is to clean the rough base material; Large quartz glass preform, characterized in that the large quartz glass tube is made as steps. 10. The quartz glass tube according to claim 9, wherein the large-size quartz glass tube is a contactless heat processing method, wherein the ratio (Do / Di) of the outer diameter (Do) and the inner diameter (Di) of the quartz glass element tube and the outer diameter of the quartz glass heat treatment tube after the heat treatment treatment ( The internal pressure is controlled so that the ratio (do / di) of do) to the inner diameter (di) is (Do / Di) / (do / di) = 1.0 to 1.5, followed by heat treatment, heating stretching or heating pressurization at 1600 to 3000 ° C. Large quartz glass preforms produced according to the stretching steps. In the method of manufacturing a large-size quartz glass preform, (a) (1) outer diameter 50-300 mm, (2) ratio of outer diameter and inner diameter 1.1-7, (3) thickness 10 mm or more. (4) a manufacturing step of preparing a large quartz glass tube having a thickness error of 2% or less and (5) an inner surface roughness of 20 µm or less; And, (b) the manufacturing process of integrating the large quartz glass tube and the optical fiber core glass rod; Method for producing a large quartz glass preform, characterized in that it comprises a. The method of claim 16, wherein the large quartz glass tube comprises: (a) opening a quartz glass base material; (b) cutting, grinding and finishing the inner and outer peripheral surfaces of the opened base material; (c) hydrofluoric its surface; And, (d) cleaning the base material subjected to the above process; A method of making a large quartz glass preform, characterized in that it is produced as steps. The method of claim 16, wherein the large quartz glass tube comprises: (a) opening the columnar quartz glass base material as a mechanical perforator; (b) cutting, polishing and finishing the inner and outer circumferential surfaces of the opened base material as an outer grinding machine and a precision honing machine; (c) immortalize the surface; And, (d) cleaning the base material subjected to the above process; A method for producing a large quartz glass preform, characterized in that the large quartz glass tube produced by the steps. 10. The method of claim 9, wherein the large quartz glass tube comprises: (a) a tubular quartz glass tube made by OVD; (b) cutting, grinding and finishing the inner and outer peripheral surfaces of the tube with an outer grinding machine and a mechanical drilling machine and / or a precision honing machine; (c) hydrofluoricating the surface; And (d) cleaning the base material through the above process; Large quartz glass preform, characterized in that the large quartz glass tube produced by the steps. The large-size quartz glass tube according to claim 16, further comprising: (a) opening the columnar quartz glass base material by hot carbon drill indentation; (b) hydrofluoricating the surface of the opened base material; And, (c) to clean the base material subjected to the above process; Method for producing a large quartz glass preform, characterized in that the large quartz glass tube produced by the steps. 17. The quartz glass tube according to claim 16, wherein the large quartz glass tube is formed of a large diameter quartz glass tube by a non-contact heating process, and a ratio (Do / Di) of the outer diameter (Do) and the inner diameter (Di) of the quartz glass tube, and the quartz glass tube. The internal pressure is controlled so that the ratio (do / di) of the outer diameter (do) and the inner diameter (di) of the quartz glass heat-treated tube obtained from is (Do / Di) / (do / di) = 1.0 to 1.5, and is 1600 to 3000 캜. Method for producing a large quartz glass preform, characterized in that the large quartz glass heat-treated tube manufactured by heat treatment, heat stretching or heat pressure stretching treatment in the. 17. The large quartz glass preform of claim 16, wherein an integration and drawing process are simultaneously performed in the same process of integrating the large quartz glass tube and the core glass rod for the optical fiber by a rod-in tube method. Manufacturing method. The optical fiber manufactured by pre-marking the large quartz glass preform of Claim 9.